1. Field of the Invention
The present invention relates to a liquid discharge head and a liquid discharge apparatus used for a printer and a video printer as an output terminal of a copying machine, a facsimile machine, a word processor, a host computer or the like. Specifically, the present invention relates to a system for a maintenance of an electro-thermal conversion element for generating bubble forming thermal energy which is utilized for discharge liquid and a liquid discharge head having a movable member which is displaced accompanied by the formation of the bubble and a liquid discharge recording apparatus mounted with the liquid discharge head and the movable member.
2. Related Background Art
Conventionally, there has been known an ink jet recording method, the so-called bubble jet recording method, wherein, by giving ink energy such as heat, the ink is allowed to produce a change of state accompanied by a rapid volume change and, by an action force resulting from this change of state of the ink, the ink is discharged from the ink discharge port, and is adhered onto a medium to be recorded so as to perform an image forming. In the recording apparatus using this bubble jet recording method, as disclosed in U.S. Pat. No. 4,723,129, there are usually arranged a discharge port for discharge the ink, an ink flow path communicating with this discharge port and an electro-energy conversion member as energy generating means for discharging the ink which is inside the ink flow path.
According to such a recording method, high quality images can be recorded at high speed with a low noise. At the same time, the head performing this recording has many excellent merits in that, because the discharge ports for discharging the ink are arranged in high density, not only recording images of high resolution but also color images can be easily acquired using a small-size device. For this reason, in recent years, this bubble jet recording method has come to be used for a number of business machines such as printers, recopying machines, facsimile machines and the like and, furthermore, even come to be used as far as in the field of an industrial system such as a textile printing apparatus or the like.
As such a bubble jet technique has become more widespread in various fields of products, in recent years, the following various types of demand for further developments have been on the rise.
For example, regarding the request for improvement of energy efficiency, optimization of a heat generating element by adjusting the thickness of the protection layer of the heat generating element can be enumerated. This method is effective in terms of improving propagation efficiency of the generated heat to the liquid.
Further, in order to obtain high quality image, there has been proposed a driving condition for giving an liquid discharge method or the like having high ink discharge speed for performing an excellent ink discharge based on a stable bubble generation or, with a view toward high-speed recording, there has also been proposed an improved shape of the liquid flow path for acquiring a liquid discharge head having high refill speed of the discharged liquid to the inside of the liquid flow path.
Furthermore, by returning to the basic principles of the liquid discharge, experimental studies have been made to provide a new liquid discharge method utilizing the bubble, a head used for that method or the like, and the liquid discharge method and the head used for that method, as disclosed in Japanese Patent Application Laid-Open No. 9-201966 specification, have been proposed.
Here, the conventional liquid discharge method and the head used for that method disclosed in Japanese Patent Application Laid-Open No. 9-201966 specification will be described with reference to FIGS. 8A to 8D and FIGS. 9 to 10. FIGS. 8A to 8D are views explaining a discharge principle in the conventional liquid discharge head, and each of FIGS. 8A to 8D is a cross-sectional view along the liquid flow path direction. FIG. 9 is a partially broken oblique view of the liquid discharge head as shown in FIGS. 8A to 8D. FIG. 10 is a cross-sectional view of a modified example of the liquid discharge head as shown in FIGS. 8A to 8D. The liquid discharge heads shown in FIGS. 8A to 8D and FIG. 10 have the most basic constitutions which control the propagation and the direction of the pressure as well as the growth direction of the bubble based on the bubble at the time of discharge liquid and improve a discharge force and a discharge efficiency. In FIG. 9, reference symbol C denotes a center of the heat generating element region.
y As used herein, xe2x80x9cupstreamxe2x80x9d and xe2x80x9cdownstreamxe2x80x9d have to do with the flow direction of the liquid from a supply source of the liquid to a discharge port through the upper direction of the bubble generating region or the constitutional direction of the liquid flow.
Further, what is meant by xe2x80x9cdownstream sidexe2x80x9d represents a discharge port side of the bubble which is taken as mainly directly acting on the discharge of the liquid droplet. To be more concrete, it means the downstream side regarding the above-described flow direction or the above-described constitutional direction against the center of the bubble, or the bubble to be generated in the region at the downstream side rather than the center of the heat generating element region. (Similarly, what is meant by xe2x80x9cupstream sidexe2x80x9d regarding the bubble itself is an upstream side regarding the above-described flow direction or the constitutional direction against the center of the bubble, or the bubble to be generated in the region at the upstream side rather than the center of the heat generating element region). Further, what is meant by xe2x80x9ccomb teethxe2x80x9d is a form in which a supporting point of the movable member is a common member and the front of a free end of the movable member is open.
In the liquid discharge head as shown in FIGS. 8A to 8D, a heat generating element 502 for allowing thermal energy to act on the liquid as a discharge energy generating element for discharge the liquid is installed at an element substrate 501. On the element substrate 501, corresponding to the heat generating element 502, a liquid flow path 503 is arranged. The liquid flow path 503 communicates with a liquid discharge port 504 and also communicates with a common liquid chamber 505 for supplying the liquid to a plurality of liquid flow paths 503 and receives an amount of the liquid matching the liquid discharged from the discharge port 504.
On the portion corresponding to the liquid flow path 503 of the element substrate 501, a plate shaped movable member 506 having a flat surface portion opposing to the heat generating element 502 is installed in the shape of a cantilevered balcony. The movable member 506 is constituted by a material such as a metal or the like having an elasticity. One end of the movable member 506 is fixed to a pedestal 507 which is formed by patterning photosensitive resin or the like on the wall of the liquid flow path 503 and the element substrate 501. In this way, the movable member 506 is supported by the pedestal 507 so as to constitute a supporting point 508 of the movable member 506.
Further, by making the movable member 506 to be comb teeth shaped, the movable member 506 can be easily prepared and yet at a low cost, and an alignment of the movable member 506 to the pedestal 507 can also be easily made. The movable member 506 has the supporting point 508 at the upstream side of a large flow which flows to the side of the discharge port 504 through the upper direction of the movable member 506 from the common liquid chamber 505 by a discharge action of the liquid, and is arranged at a distance of about 15 xcexcm apart from the heat generating element 502 in a position opposing to the heat generating element 502 such as to conceal the heat generating element 502 so that it has a free end 509 to this supporting point 508 in the downstream side. This space between the heat generating element 502 and the movable member 506 becomes a bubble generating region 510.
Next, the action of the liquid discharge head constituted as described above will be described with reference to FIGS. 8A to 8D.
First, in FIG. 8A, the insides of the bubble generating region 510 and the liquid pass 503 are filled with the ink.
Next, in FIG. 8B, by allowing the heat generating element 502 to produce heat, heat acts on the liquid of the bubble generating region 510 between the movable member 506 and the heating element 502 and that liquid is allowed to generate a bubble 511 based on a film boiling phenomenon as mentioned in U.S. Pat. No. 4,723,129. The pressure based on the generation of the bubble 511 and the bubble 511 preferentially acts upon the movable member 506, and the movable member 506 is largely displaced so as to open at the side of the discharge port 504 with the supporting point 508 as a center as shown in FIG. 8B, FIG. 8C or FIG. 9. Because of the propagation of the pressure based on the generation of the bubble 511 by the displacement or the displaced state of the movable member 506 and the top end of the bubble 511 having a width, a bubbling power of the bubble 511 is easily guided to the side of the discharge port 504 and fundamental improvement of a discharge efficiency and a discharge force of the liquid droplet or a discharge speed can be attempted.
As described above, the technique mentioned in Japanese Patent Application Laid-Open No. 9-201966 specification or the like is a technique where the physical relationship between the supporting point and the free end of the movable member is changed to the relationship in which the free end of the movable member is positioned at the discharge port side, that is, at the downstream side and where, by arranging the movable member to face the heat generating element or the bubble generating region, the bubble is actively controlled.
Each configuration of an element substrate 601 of the liquid discharge head, an heat generating element 602, a liquid flow path 603, a discharge port 604, a common liquid chamber 605 and a bubble generating region 609 as shown in FIG. 10 are each the same as in the liquid discharge head as described based on FIG. 8 and the description thereof will be omitted.
In the liquid discharge head as shown in FIG. 10, at one end of the movable member 606 which is formed in the shape of a cantilevered balcony, a stepped portion 606a is installed, and, on the element substrate 601, the movable member 606 is directly fixed. In this way, the movable member 606 is held on the element substrate 601 so as to constitute a supporting point 607 of the movable member 606, and a free end 608 is constituted in the downstream side to this supporting point 607.
As described above, by installing a pedestal at the fixed portion of the movable member or by installing the stepped portion to the fixed portion of the movable member, a gap of about 120 xcexcm is constituted between the movable member and the heating portion, thereby sufficiently drawing out the effect of improving the liquid discharge efficiency by the movable member. Consequently, according to the liquid discharge head based on the discharge principle as described above, synergistic effects with the bubble generated and the movable member displaced by this bubble can be obtained, and the liquid in the vicinity of the discharge port can be effectively discharged, so that the discharge efficiency of the liquid is improved in contrast to the discharge method and the liquid discharge head of the conventional bubble jet system which does not use the movable member.
As described above, in the liquid discharge head having the movable member and the recording apparatus provided with the head, the present inventors in the process of seeking the effect obtainable from the mobility of the movable member (which is also referred to as xe2x80x9cvalvexe2x80x9d) to the highest possible level found that, in order to secure high longevity, high reliability or the like of the valve action, it is necessary to maintain a movable load of the valve, while attempting to protect the movable member and stabilize the liquid discharge system by estimation of the ambient air temperature of the valve, the detection thereof or the like.
That is, in the process of studying to provide the movable member itself with high level which exceeds the life of the electro-thermal conversion element, when discharge endurance/change of performance of the head were being observed, a change was developed in the discharge itself at a certain time, and a phenomenon occurred in which the stable discharge at high frequency driving which is one of the effects of the valve becomes unstable.
In spite of the rigid design of the valve being performed for optimizing not only the valve action but also the head efficiency, there have been found significant differences between the valve action in a state of being normally supplied with the ink inside the recording head and the valve action in a state of being not supplied with the ink, and its the valve life. Here, what is meant by the state of being not supplied with the ink is a non-discharge phenomenon (a state in which the ink is not normally discharged(ejected)) where, in the course of the continuous discharge by the recording head, the minute bubbles existing in the ink supply pass are mixed into a nozzle accompanied with the ink supply refill at a time of the continuous discharge, thereby causing the ink to run out partially at each nozzle, or a phenomenon where the minute bubbles gather in an ink liquid chamber at the rear of the nozzle or the bubbles grow into big bubbles by the temperature rise due to the driving of the heat generating element so that the bubbles are drawn into a number of nozzles accompanied by the ink supply refill at a time of the continuous discharge, thereby leading a number of nozzles to continuous non-discharge. The present inventors in the course of the experimental studies and observations found the following relationships between the action and the life of the valve member.
In the case where the ink does not exist at all inside the liquid flow path of the nozzle, when the driving of the heat generating element is performed, in spite of the fact that the valve member does not act, the life of the valve member is sometimes reduced. This is because, during the image data is being printed when the heat generating element falls into this state during continuous discharge, the heat generating element is continuously heated in a state of being unable to secure the so-called heat loss effect which is to take and exhaust the heat of the head when the ink is discharged and the temperature of the element substrate having the heat generating element and the valve member rapidly rises and attains high temperature which is not reachable in a state where the ink normally exists. Further, after this state continues for a while, when the ink, which is at ordinary temperature, is supplied into the nozzle, stress on the valve member resulting from instantaneous thermal shock, promotes the development of rigidity and material fatigue. Similarly, when ink is supplied at a high temperature which is not reachable in the ink""s normal state, an excessive film boiling due to the state of high temperature is generated, which is different from the film boiling desired to be generated by a controlled pulse applied to achieve discharge, and, in particular, the valve member having a pedestal or the like at its fixed portion is instantaneously subjected to an unimaginable valve displacement, resulting in that physical stresses on the pedestal or the like.
This phenomenon shows a tendency toward the situation in which fatigue of the valve member in the absence of ink in creases with the shape where the displacement stress to the valve member by the valve mobility is larger, and, in the worst case, it was ascertained that the phenomenon also leads to fatigue defects due to the generation of cracks or the like in the movable member itself.
In this way, it was confirmed that, as the discharge in a state where the ink is not supplied to the inside of the recording head (hereinafter, referred to as xe2x80x9cempty dischargexe2x80x9d or xe2x80x9cempty printingxe2x80x9d) is repeated many times, the fatigue of the valve portion develops its effect at an early stage; therefore, in order to avoid this problem, it was recognized that employment of the maintenance system for avoiding empty discharge and empty printing and thus limiting fatigue of the valve member to the smallest possible minimum is the most important problem in terms of achieving still more reliability and durability.
In order to realize this problem, irrespective of whether the recording head is in the midst of stand-by for printing or during printing, the state of the ink inside the recording head chip is detected, and, if the ink supply is not normal, for example, if the ink supply is in a defect state, the discharge signal is shut off in the early stage so as to prevent the empty discharge or printing defect, It was found that when the defect state of the ink supply can be estimated, forced deaeration of the bubble inside the recording head by suction means provided for the recording apparatus can prevent the empty discharge.
Accordingly, the present invention provides a movable valve protection method aimed at preventing the fatigue defects in the valve member due to repeated empty discharge as described above and securing high longevity or high reliability of not only the movable valve but also of the head; this may also be considered to be a movable value durability improvement method. Also provided are an ink jet head structure and an ink jet recording apparatus.
The present invention provides a system, where in order to control accumulation of the stresses in the displacement of the movable member and thermal shock stresses to the smallest possible minimum, by judging whether there has been a liquid supply failure, intrinsic characteristics of the movable member are secured, and by utilizing even anticipated and estimated level of a failure from the substantial detection of the liquid supply failure, a safety factor can be enhanced.
In order to attain the above-described object, the present invention provides a liquid discharge head including: a discharge port for discharge liquid; a liquid flow path communicating with the above-described discharge port having a bubble generating region for generating a bubble in the liquid inside said bubble generating region; a discharge energy generating element for generating thermal energy for generating the bubble in the liquid inside the above-described bubble generating region; and a movable member which faces the above-described discharge energy generating element spaced apart from the above-described discharge energy generation and in which an end portion at the upstream side in the flow direction of the liquid inside the above-described liquid flow path is fixed and a downstream end is a free end, in which the ink is discharged from the liquid discharge head and a recording is performed by adhering the above-described liquid on the medium to be recorded, and in which, based on means for detecting the ink supply state inside the above-described liquid flow path and the detection result of the ink supply state inside the above-described liquid flow path, if a judgment is made that the ink is in a state of being not normally supplied, means for controlling or stopping the driving to the above-described discharge energy generating element is provided.
Means for detecting the above-described ink supply state is considered to be temperature detection means for detecting a temperature rise per unit time inside the liquid flow path.
Further, the present invention includes a liquid discharge apparatus having a liquid discharge head such as the above-described and a driving signal supply means for supplying a driving signal for discharge the liquid from the liquid discharge head and, furthermore, a liquid discharge apparatus having a liquid discharge head such as the above-described, medium to be recorded conveyance means for conveying a medium to be recorded which receives the liquid discharged from the liquid discharge head. In these liquid discharge apparatuses, those performing the recording by discharge the ink from the above-described liquid discharge head by adhering the above-described ink on the medium to be recorded are preferable.
Furthermore, the present invention relates to a valve protection method of a liquid discharge head having a heat generating element inside a liquid flow path communicating with a discharge port and a movable plate for directing a bubble growing by a film boiling on said heat generating element to a side of said discharge port, in which an ink supply state inside said liquid flow path is detected and the driving to said heat generating element is controlled or stopped when a judgment is made that the ink is not normally supplied based on a detection result of said ink supply state.
Further, the present invention relates to a valve protection method of the liquid discharge head having the heat generating element inside the liquid flow path which communicates with the discharge port and a movable plate for directing the bubble growing on the heat generating element by the film boiling toward the side of the above-described outlet, wherein, when the temperature rise inside the above-described liquid flow path is detected and that temperature rise is more than a predetermined threshold value, a judgment is made that the ink is in a state of being not normally supplied and the driving to the above-described heat generating element is controlled or stopped.
In such a configuration of the present invention, the ink supply state of the liquid flow path where the movable member (movable valve) is arranged is estimated or detected and, if the ink supply state is not normal, the driving of the heat generating element is controlled or stopped so that it is possible to prevent the empty discharge or the empty printing of the recording head at an early stage and limit the displacement stress to the movable member to the smallest possible minimum.
Regarding the judgment method of the liquid supply failure state of the present invention, a judgment is made on the liquid supply failure by judging abnormality of the temperature rise of the liquid chamber inside the head (in the case of plurality of nozzles, referred to as common liquid chamber) for supplying the liquid to the flow path (nozzle) in which the electro-thermal conversion element is located, or employment of the flow path sensor or CR sensor as mentioned in Japanese Patent Application Laid-Open No. 10-109430 specification or temperature rise detection means to be described later and like for judging the liquid state inside the liquid supply member for maintaining the liquid for use of the liquid supply to the head and the liquid state in the supply route can be adopted, and these sensors and detection means can be utilized as an information source in terms of the prohibition or the limitation of the displacement of the movable member.